C++: Remove redundant transitive closure#21314
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MathiasVP merged 1 commit intogithub:mainfrom Feb 12, 2026
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Pull request overview
Reduces the risk of catastrophic compiler behavior on very large C++ codebases by simplifying the flowsToBackEdge predicate in the internal IR dataflow utilities, aiming to avoid constructing an overly large transitive closure.
Changes:
- Removes a transitive-closure-based condition from
flowsToBackEdge. - Replaces the previous successor/dominance combination with a single
strictlyDominatesdominance check.
aschackmull
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Feb 12, 2026
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I agree, this certainly looks redundant.
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The
doublyBoundedFastTCproduced by the compiler for this transitive closure was too large and failed withcaught com.semmle.util.exception.CatastrophicError: Failed to expand RoaringCharList of size 2147483638 to make space for 3 more elements while evaluatingon a very large Microsoft repository.This makes sense as the end-points for this transitive closure aren't really very restricted. However, luckily this whole transitive closure should be redundant since we have SSA flow from an element in
bb1to another element inbb2, and sobb2should be a control-flow successor ofbb2by the correctness of SSA.